The standard room sizes on Carnival ships are 185 sq ft. Which is typically larger in comparison to NCL and RCCL ships. As far as the width of the ship, the Pride is 106 ft wide versus the SKy at 105.8 ft. The Pride is 88,500 GRT while the sky is 77,104 GRT. So you have nothing to be concerned about with respect to the ship, you are getting a larger ship with equivalent or better on board amenities. I'm not going to get into a discussion about which cruise line is better than the other. That is a personal preference thing, but I can say that if you are good on your first NCL cruise, then you will more than enjoy your first Carnival cruise.
The Pride is a Spirit class ship, and I love the Spirit class design. It is a very well thought out design. You will have a great time, so stop worrying about it.
Carnival Cruise Lines:
Fantasy 90, Celebration 95, Victory 05, Conquest 05, Spirit 6/06, Freedom 6/08, Holiday 7/08, Victory 6/09, Valor 9/09, Dream 6/10, Splendor 8/10,Conquest 8/11,Magic 11/11,Triumph 4/12,Spirit 7/12,Freedom 11/12, Triumph 2/13 - The fire cruise
NCL Dream October 2006, RCCL Mariner OTS June 2007